From: Roman Gushchin guro@fb.com
[ Upstream commit 7a1adfddaf0d11a39fdcaf6e82a88e9c0586e08b ]
It was reported that on some of our machines containers were restarted with OOM symptoms without an obvious reason. Despite there were almost no memory pressure and plenty of page cache, MEMCG_OOM event was raised occasionally, causing the container management software to think, that OOM has happened. However, no tasks have been killed.
The following investigation showed that the problem is caused by a failing attempt to charge a high-order page. In such case, the OOM killer is never invoked. As shown below, it can happen under conditions, which are very far from a real OOM: e.g. there is plenty of clean page cache and no memory pressure.
There is no sense in raising an OOM event in this case, as it might confuse a user and lead to wrong and excessive actions (e.g. restart the workload, as in my case).
Let's look at the charging path in try_charge(). If the memory usage is about memory.max, which is absolutely natural for most memory cgroups, we try to reclaim some pages. Even if we were able to reclaim enough memory for the allocation, the following check can fail due to a race with another concurrent allocation:
if (mem_cgroup_margin(mem_over_limit) >= nr_pages) goto retry;
For regular pages the following condition will save us from triggering the OOM:
if (nr_reclaimed && nr_pages <= (1 << PAGE_ALLOC_COSTLY_ORDER)) goto retry;
But for high-order allocation this condition will intentionally fail. The reason behind is that we'll likely fall to regular pages anyway, so it's ok and even preferred to return ENOMEM.
In this case the idea of raising MEMCG_OOM looks dubious.
Fix this by moving MEMCG_OOM raising to mem_cgroup_oom() after allocation order check, so that the event won't be raised for high order allocations. This change doesn't affect regular pages allocation and charging.
Link: http://lkml.kernel.org/r/20181004214050.7417-1-guro@fb.com Signed-off-by: Roman Gushchin guro@fb.com Acked-by: David Rientjes rientjes@google.com Acked-by: Michal Hocko mhocko@kernel.org Acked-by: Johannes Weiner hannes@cmpxchg.org Cc: Vladimir Davydov vdavydov.dev@gmail.com Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Linus Torvalds torvalds@linux-foundation.org Signed-off-by: Sasha Levin sashal@kernel.org --- Documentation/admin-guide/cgroup-v2.rst | 4 ++++ mm/memcontrol.c | 4 ++-- 2 files changed, 6 insertions(+), 2 deletions(-)
diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/admin-guide/cgroup-v2.rst index 184193bcb262..5d9939388a78 100644 --- a/Documentation/admin-guide/cgroup-v2.rst +++ b/Documentation/admin-guide/cgroup-v2.rst @@ -1127,6 +1127,10 @@ PAGE_SIZE multiple when read back. disk readahead. For now OOM in memory cgroup kills tasks iff shortage has happened inside page fault.
+ This event is not raised if the OOM killer is not + considered as an option, e.g. for failed high-order + allocations. + oom_kill The number of processes belonging to this cgroup killed by any kind of OOM killer. diff --git a/mm/memcontrol.c b/mm/memcontrol.c index e79cb59552d9..07c7af6f5e59 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -1669,6 +1669,8 @@ static enum oom_status mem_cgroup_oom(struct mem_cgroup *memcg, gfp_t mask, int if (order > PAGE_ALLOC_COSTLY_ORDER) return OOM_SKIPPED;
+ memcg_memory_event(memcg, MEMCG_OOM); + /* * We are in the middle of the charge context here, so we * don't want to block when potentially sitting on a callstack @@ -2250,8 +2252,6 @@ static int try_charge(struct mem_cgroup *memcg, gfp_t gfp_mask, if (fatal_signal_pending(current)) goto force;
- memcg_memory_event(mem_over_limit, MEMCG_OOM); - /* * keep retrying as long as the memcg oom killer is able to make * a forward progress or bypass the charge if the oom killer